The invention relates to producing shale oil and related mineral materials from subterranean deposits of oil shale.
Numerous subterranean oil shales are mixed with water-soluble minerals and comprise substantially impermeable, kerogen-containing, earth formations from which shale oil can be produced by a hot fluid-induced pyrolysis or thermal conversion of the organic solids to fluids. A series of patents typified by the T. N. Beard, A. M. Papadopoulos and R. C. Ueber U.S. Pat. Nos. 3,739,851; 3,741,306; 3,753,594; 3,759,328; and 3,759,574 describe procedures for utilizing the water-soluble minerals to form rubble-containing caverns in which the oil shale is exposed to a circulating hot aqueous fluid that converts the kerogen to shale oil while dissolving enough solid material to expand the cavern and expose additional oil shale. In such processes, the heat transfer is aided by injecting the hot fluid into an upper portion and withdrawing fluid from a lower portion of the cavern.
However, as described in the P. J. Closmann and G. O. Suman U.S. Pat. Nos. 3,804,169 and 3,804,172, such prior cavern-utilizing processes are subject to a tendency for the flow paths to become plugged. The hot aqueous fluid flowing down along the walls of the cavern rubbles and disaggregates portions of the shale oil into particles having sizes ranging from a few microns to several feet in diameter. The particles tend to slump or to flow as a turbidity current down the walls of the cavern and pile up around the fluid withdrawal point near the bottom of the cavern. In the U.S. Pat. No. 3,804,169, a pattern of fracture-interconnected caverns and wells are arranged so that fluid injected near the top of one well is produced through a plurality of surrounding wells with the flow rates being too low to carry the solids to the production wells. In the U.S. Pat. No. 3,804,172, the lower portion of such a cavern is packed with a mass of large rigid solid particles, so that the slurried solids in the slumping turbidity currents are spread over large surface areas while the fluids are flowing through the relatively large openings that exist between the particles.
In the process of patent application Ser. No. 489,639, filed July 18, 1974 by M. J. Tham and P. J. Closmann, now U.S. Pat. No. 3,880,238, a hot solvent-fluid (which is significantly miscible with at least one organic or inorganic solid or liquid pyrolysis product of the oil shale) is injected into an upper portion of a rubble-containing cavern in a subterranean oil shale. A non-solvent gas (which has a relatively insignificant miscibility with any of said pyrolysis products) is also injected into an upper portion of the cavern. Fluid is withdrawn from the cavern from below the points of fluid injection. And, the properties and flow rates of the injected and produced fluids are correlated so that the cavern remains sufficiently liquid-free to prevent a significant plugging of the fluid flow path.